122 B. L. STREHLER 



conditions which should promote iitiUzation or decrease production of 

 these products decrease the intensity of luminescence. 



3. The induction curves are due to changes in concentration of a 

 numlier of intermediates in the chain of reactions leading from the 

 photochemical events to CO2 fixation, including the formation and 

 utilization of ATP. 



4. The decay curves suggest that two molecular species (probably 

 on the reductant side) are capable of eliciting luminescence. The 

 short-lived component may be regarded as the primary photoproduct 

 and the longer lived component as a substance derived from the first 

 and representing a later hydrogen or OH carrier in the photosyn- 

 thetic sequence. It is interesting that the short- and long-lived com- 

 ponents behave kinetically similarly to the various constants derived 

 from flashing light experiments and thus mixtures of different life- 

 time intermediates may be responsible for the discrepant results 

 reported by various authors (15-18) under differing conditions of 

 illumination, flash duration, etc. 



Acknowledgments. I wish to acknowledge with thanks many stimulating 

 discussions with Drs. William Arnold, James Franck, and Hans Gaffron on 

 the subject material here summarized. It should be emphasized that some of 

 the detailed interpretations here set forth are in conflict with parallel inter- 

 pretations of Drs. Franck and Brugger of this laboratory, although we are in 

 agreement about the general nature of the process. 



Discussion 



Rabinowitch : Does this mean that one curve is first order and the other curve 

 is zero order? 



Strehler: The best information (Arnold's work) would indicate that, with a 

 very brief flash, one obtains a second-order decay. But, when one uses a longer 

 flash, he obtains something that is neither first nor second order but in between. 



Wassink: I would like to ask just one question; namely, how does any con- 

 sideration of the triplet state of the chlorophyll come into this? 



Strehler : I don't think it is necessary, on the basis of the information we have, 

 to postulate anything about triplet states. I think that should await a better 

 understanding of what the natures of the intermediates are. 



Wassink : If a triplet state is involved, it must come in between your chemistry 

 and luminescence, just as it must for fluorescence. 



Strehler: I believe so — yes. 



"Wassink: You don't see any objection? 



Strehler: I see no objection, but I probably am not (lualified to make the judg- 

 ment. 



